1. Field of the Invention
This invention relates to apparatus and methods for addressing out-of-space conditions in Virtual Storage Access Method (VSAM) volume data sets (VVDSs).
2. Background of the Invention
In the z/OS operating system, Virtual Storage Access Method (VSAM) volume data sets (VVDSs) are data sets that describe the characteristics of VSAM and Storage Management Subsystem (SMS) managed data sets residing on direct access storage device (DASD) volumes. These VVDSs typically reside on the same volumes where the VSAM and SMS-managed (non-VSAM) data sets reside. Every volume containing VSAM or SMS-managed data sets will typically contain a VVDS to describe the data sets that are stored thereon.
A VVDS typically contains three types of entries, or records: a VSAM volume control record (VVCR) that contains BCS back pointers and information to manage DASD space; a VSAM volume record (VVR) for each VSAM data set on the volume and containing information about the VSAM data set; and a non-VSAM volume record (NVR) for each non-VSAM data set on the volume and containing information about the non-VSAM data set.
VVDS access is required whenever VSAM data sets and SMS-managed data sets are processed (e.g., read from, written to, updated, etc.) on DASDs. This requires physical I/O to the volume(s) where the data sets reside, both to access the VVDS as well as the data sets described in the VVDS. Unfortunately, if a VVDS cannot be updated because the VVDS has run out of space (e.g., because it has reached its maximum size and cannot store any more entries), new data sets cannot be added to the volume. Existing data sets described in the VVDS and currently stored on the volume may also become inaccessible.
When an application is allocating or accessing a data set on a volume and the VVDS on the volume runs out of space, an error will occur and the application may receive an error message (e.g., an IDC3009I 50-30 error message in the z/OS operating environment). This error will cause an application outage since the application will be unable to access data on the volume. To resolve the error, a user is instructed to either (1) delete data sets from the volume (to free up space in the VVDS), or (2) create a new larger VVDS and recover all data sets to the volume from a backup. The first option may be infeasible since deleting data sets may be time-consuming and delete valuable data. The second option may be undesirable at least partly because of application downtime. The second option is also hindered by the fact that creating a new VVDS on the volume requires adding a record to the existing VVDS. Since the existing VVDS is full, such a record cannot be added.
In view of the foregoing, what are needed are apparatus and methods to more effectively address out-of-space conditions in VVDSs. Ideally, such apparatus and methods will avoid or minimize application outages.